1. Field of the Invention
The present invention relates to an eddy current inspection device, an eddy current inspection probe and an eddy current inspection method for detecting a characteristic change of an inspection target (test object) such as a flaw or a change in material quality occurring on the surface or inside of the inspection target.
2. Description of the Related Art
The eddy current inspection method involves detecting a characteristic change such as a flaw or a change in material quality (hereinafter referred to as a “defect”) occurring on the surface or inside of the test object by measuring a change in an eddy current caused in the test object by time-varying magnetic fluxes. The time-varying magnetic fluxes are generated by use of an excitation coil placed in the vicinity of the surface of the test object by applying time-varying electric current (excitation current) to the excitation coil.
Conventional techniques employing the eddy current inspection method include, for example, a technique disclosed in JP-05-99901-A in regard to an eddy current inspection device. The eddy current inspection device according to JP-05-99901-A comprises a plurality of excitation coils, rotational magnetic field generating means, a plurality of detection coils, and flaw detection means. The excitation coils are attached to a magnetic core and arranged at fixed angular intervals for the purpose of detecting the presence/absence of a defect and the direction of each defect in a flat metal plate, etc. The rotational magnetic field generating means magnetically excites the excitation coils with a signal generated by amplitude modulation by use of AC voltage and thereby applies a rotational magnetic field to the test object. The detection coils are arranged on the magnetic core corresponding to the excitation coils in order to detect a magnetic field generated from the test object according to an eddy current occurring in the test object. The flaw detection means detects defects existing in the test object based on output signals from the detection coils.